Tuesday, March 4, 2014

Holding pattern orientation and circling naming conventions

I received a great e-mail from a listener to the interview in San Diego.  As I write this it's 9 degrees (F) here in Dayton, Ohio, so I'm wishing I was in San Diego!

He asks the following:

First, I fly around San Diego and it seems most published missed approach holds require a parallel/teardrop entry.  Why are they not designed for a direct entry?

Second, The city of San Diego has multiple airports, KSAN, KSEE, KMYF, KSDM. KSEE has a LOC-D approach.  The -D signifies it's the fourth LOC approach. My question is whether it's the fourth LOC approach into KSEE, or is it the fourth LOC approach for the city of San Diego?

Wouldn't it be nice if all holds were a direct entry?  Sure would, but that hardly ever seems to be the case, doesn't it?

There are several considerations when designing missed approach holding patterns (roughly in priority order, though this is not found in the regulations):
1. Signal reception for course guidance and crossing radials (if applicable).
2. Surrounding terrain (usually the most critical consideration).
3. Surrounding airspace.
4. ATC procedures/traffic flow/sector boundaries.
5. Ease of flying another procedure once in the holding pattern.
6. Existence of already-established holding patterns at the same fix.
7. Ease of entry into the holding pattern.

1-4 are fairly self-explanatory.  For #5, there is a pertinent requirement in the regulations (FAA 8260.3B, para 291): 

"Whenever practical, holding patterns should be aligned to coincide with the flight course to be flown after leaving the holding fix".  

I consider this the "what are you going to do next" clause.  So you're in holding, but you don't want to stay there forever.  It's nice if the inbound course for the hold lines up with, say, another (or even the same) approach procedure.  For example, many RNAV (GPS) approaches have the missed approach go to the IF for the RNAV (GPS) approach to the opposite runway.  The holding pattern will often be oriented so that once established, you could fly the opposite approach from that point. 

Case in point - KOJA (Weatherford, OK), RNAV (GPS) RWY 17 and 35.  Fly one, go missed to the IF for the other one, turn around and repeat. You can see-saw back and forth all day flying one procedure after the other if you like.

Many ILS and LOC procedures have the missed approach take you back to the FAF and hold, perfectly lined up for another try. 

The same is often true of VOR approaches where the VOR is the FAF. Sometimes, though, especially in mountainous areas, holding patterns just appear cockeyed for no reason.  Often in these situations, terrain forces the orientation - just a few degrees one way or the other may make all the difference in the holding pattern altitude.

For reason #6 above, a good example is if the holding is at a VOR, there may already be other holding patterns at that fix - to reduce confusion, any new patterns may be oriented the same direction.  Or they may not - depends on the exact situation. 

Notice that "ease of entry" is typically the last consideration.  This reflects the reality that holding procedures just aren't flown much on non-training flights - ATC will more typically issue its own set of missed approach instructions, usually using radar vectors.  Also, since it has to be presumed that IFR pilots are capable of flying any type of hold entry, the importance of this consideration is reduced to a "nice, but not necessary" level.

An additional note on this - holding patterns are BIG when compared to the speeds we typically fly in IFR training.  A Cessna 172 flying a 1-minute holding pattern in no wind will generally stay within about 2 nm of the fix at all times, even allowing for turns.  Holding pattern airspace increases with altitude, but the smallest holding patterns in use by the FAA are ovals about 14.4 nm long and 8.8 nm wide, with an additional 2 nm buffer area on all sides!  This size is required to contain faster aircraft with correspondingly larger turn radii.  So even though the pattern might look like it's well clear of obstacles/airspace/traffic flow, it might not be for all aircraft.

For the second question, there are two rules in effect here, from FAAO 8260.19F, para 4-1-5f:

(1) Do not duplicate the alphabetical suffix for circling procedures at an individual airport to identify more than one circling procedure. If more than one circling procedure exists, and regardless of the final approach alignment or type of facility, use successive suffixes.


(2) The alphabetical suffix for circling procedures must not be duplicated at airports with identical city names within one state. Regardless of the airport name, successive suffixes must be used for all airports that serve the same city.

There is another clause in FAAO 8260.3B, para 162:

"a revised procedure will bear its original indentification".

Presumably, at least at one time there were already -A, -B, and -C circling procedures to airports serving San Diego, so the KSEE LOC circling was labeled the LOC-D.  I cannot find a -B or -C at any of the civilian airports, but given the rule above, it's likely there were at one time. Once the KSEE LOC-D was named, any further amendments are supposed to keep that name, to reduce confusion.

Thanks for the great questions!

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